Power Supply Resevoir Size

[Lazy Cat]

We all probably agree that fully charged high capacity accumulator's pack is as best as we can provide for an amplifier's power supply. What we try here is to mimic an ideal voltage source, for which accumulator is as closest possible approximation as we can get in reality. Lowest power supply source resistance and instant limitless current capability should be our goal, anything from being cheap. How come closest to that ideal power supply and to still maintain inside reasonable costs is the main question. There's no ideal solution, as always optimization is the key word.

[AP2]

Certainly agree that a good design with psu transformer sounds good. commercially know well some professional big amplifiers, realized with a transformer per channel and large capacitors. I realized that the speech was focused to obtain performance even closer to the dynamic reality. in this case it is necessary to obtain a supply regulation, this independent if analog or smps. I think that on this point we all agree. is different (and I do not agree) that the regulated power supply fast, is not better. this is the point.

[tsiros]

Originally Posted by AP2

speech

in roman languages, ratio and oratio are different words with different meanings.

which is absurd. In greek though, thought, word(vocalisation) and script are all one word: λόγος. Because it is absurd to think one thing, say another and finally write a third thing.

keep that in mind, it will help you not get confused later on

[jean-paul]

Well IMO it is absurd that thought, word(vocalisation) and script are all one word: λόγος. This because they are all different things.

[gootee]

Originally Posted by AP2

I started a thread that talks about the geometry of the signals. the conclusion?
those who are not able to understand, they think that I am a charlatan.
then there are those who understand well, then attack me.

the conclusion is real one. amplifier to modulate the current. values ​​of this modulation (according to the dynamics of the source) shall have a right to reconstruct the sound. this can not happen if the supply rails decreases.
this is actually a sub reverse modulation, perfect to change the shape of the signals, right where it defines their speed. (just it is timbre of instument's)
So the power supply must be stabilized, but this requires a high-speed controller. does not make sense to see the ripple, eg. at 100Hz. looks at the rising edge of a square wave also.
I add...that the psu, decides fidelity in reproducing sounds, especially all the sounds that form their characteristic dynamics.
This is not woodo or market convenience, this is science very clear.

AP2,

I am certain that you already know all of this. But it is one of my currently-active areas of interest. So it would have been difficult for me to have not commented.

Please know that I am not quite an expert at any of this (yet). But I have formed a few ideas, which follow, below. For ease of construction, I will just state everything as if it is known to be true. But I am always trying to learn and therefore being shown what is wrong with my thinking is one of the most valuable results I could get, here.

-----

You're close. But the PSU voltage is not the music signal. The PSU current is the music signal.

The capacitors are there to supply current accurately and precisely, when the power transistors lower and raise their channel-resistance in response to the small-signal music control signal.

The power supply voltage variations would be important if PSRR was not good, because the transistor's varying channel-resistance would then not produce a linearly-varying current vs the (base or gate) control signal if the psu voltage that pushes the current was not constant.

Moving on, now also consider the parasitic inductance and resistance of the conductors from the PSU to the power output devices and consider the impedance AS SEEN BY the power pin of the output device and the ground pin of the load (which is the ONLY place it matters). No matter how brilliantly-engineered a PSU or regulator is, i.e. no matter how low its output impedance vs frequency is, it will be partially ruined by anything more than a few centimeters (or less) of wire or PCB trace, especially at the high frequencies that are essential for both closed-loop response speed (with accuracy) and also the precise temporal accuracy of signal-current delivery (visualize the compact-form Fourier components (i.e. with phase angle) of a complex signal and imagine their phase angle accuracy and their "amplitude versus time" accuracy deteriorating as frequency increases. Edges would become blurred and the precise relative timing cues would be lost, degrading the clarity or even the existence of the soundstage imaging, and also the reproduction accuracy of the true nature of each type of sound.

The necessary solution for the highest frequencies must be very-closely-mounted decoupling capacitance, with very-low-impedance connections, right at the points of load for each such device. Next must be one of either a) the PSU or regulator itself, with only a few centimeters (or less) of leads to each power device, OR, b) larger local decoupling capacitances.

The very-local decoupling capacitors would be able to supply the fast transient currents that are needed when a transistor suddenly "opens wider". However, they might often need to be implemented as parallel sets of smaller capacitors, in order to achieve a low-enough impedance to a high-enough frequency. Using multiple [parallel copies of both power and ground rails, from PSU to load, can also be very helpful in maintaining a low-enough impedance, as seen by the load.

If there were no local supply of current and those fast transient currents had to move through the inductances of the power and ground conductors from the power supply or regulator, then they would a) be late arriving, and b) would create relatively-large disturbances in the power rail voltage and the ground rail voltage (the amplitude of which would depend on the time-rate-of-change of the current, not on its amplitude, which means that very "small" currents could create large voltage disturbances, if the currents were fast-changing).

OK. I'll just quit for now.

Cheers,

Tom

[ChrisA]

Originally Posted by AP2

Certainly agree that a good design with psu transformer sounds good. commercially know well some professional big amplifiers, realized with a transformer per channel and large capacitors. I realized that the speech was focused to obtain performance even closer to the dynamic reality. in this case it is necessary to obtain a supply regulation, this independent if analog or smps. I think that on this point we all agree. is different (and I do not agree) that the regulated power supply fast, is not better. this is the point.

None of this is hard until you have a budget. No matter what the budget, and you can build an amp for $100 or $500 or $1,000 as soon as you fix the price then you have to always think in terms making one thing bigger makes something else smaller. More filter caps means yo have to reduce the transformer or the size of the heatsink

This is where real engineers earn their pay. For example anyone could design a bridge over a canyon, simply fill the canyon with concrete. Gets a LOT harder when you want to minimize the cost. Same with amps. It is pretty easy to simply toss in the most expensive parts you can find and build an amp. But let's say the goal was "The best you can build for $250 and the specs are to power a pair of 87dB/W speakers in a 20 foot square room and the use like classical music at 'moderate' volume." Now you have a hard problem and it is not easier if the budget is $500.

[ChrisA]

Originally Posted by gootee

...
If there were no local supply of current and those fast transient currents had to move through the inductances of the power and ground conductors from the power supply or regulator, then they would a) be late arriving, and b) would create relatively-large disturbances in the power rail voltage and the ground rail voltage (the amplitude of which would depend on the time-rate-of-change of the current, not on its amplitude, which means that very "small" currents could create large voltage disturbances, if the currents were fast-changing).

A fun project is to model this in Spice. First use a "perfect" voltage source and then run the model again placing a resistor and inductor in series with the perfect power supply and ground return. Choose an inductor and resistor value to match with a one foot length of wire has. The effect that we hear is not really caused so much by the wire alone but is that if combines with the capacitance of the transistor to form a low pass filter.

A qick and easy "fix" is to place a small film by-pass cap directly on the transistor pin. Pretty much like you do when you build with ICs

[gootee]

Originally Posted by ChrisA

A fun project is to model this in Spice. First use a "perfect" voltage source and then run the model again placing a resistor and inductor in series with the perfect power supply and ground return. Choose an inductor and resistor value to match with a one foot length of wire has. The effect that we hear is not really caused so much by the wire alone but is that if combines with the capacitance of the transistor to form a low pass filter.

A qick and easy "fix" is to place a small film by-pass cap directly on the transistor pin. Pretty much like you do when you build with ICs

Do you mean a model kind of like the one at http://www.diyaudio.com/forums/solid...ml#post3117339 ? <grin>

[MagicBox]

Don't stop Tom,

That was an excellent summary of what this thread is about and it's great to see the PSU gets a well deserved analysis as well, besides the ever prevalent THD numbers haha

[AndrewT]

Chris A must have fallen asleep for the last 20days.